PURPOSE: To detect abnormality of a breaker even if an electromagnetic coil is broken by dividing the terminal voltage across the electromagnetic coil and measuring the operation time of electric equipment from the voltage division output.

CONSTITUTION: A breaking mechanism which is not shown in a figure is operated through the lead-out coil 1 of the breaker 1 and a switch 2 is opened to cut off electric feeding to the coil 1. The terminal voltage across the coil 1 is divided to develop a voltage proportional to the coil voltage across a resistance 6b, and the voltage is inputted to a decision means 4. The output of a comparator 8 is supplied to a timer 9, whose pulse time width is measured. This pulse time width is monitored by a decision device 10 to judge whether the breaker is normal or not. Then if the coil 1 is broken, a voltage is developed across the coil 1, but the breaking mechanism does not operate, so the switch 2 is not opened. The pulse time width measured by the timer 9, therefore, increases abnormally, so the fault of the breaker is detected from the time width of the pulse even if the coil is broken.